The aim of this work is to examine assets and drawbacks of hybrid RANS-LES calculations for passenger compartment airflow using a generic mock-up model. The evaluation will focus on Scale-Adaptive Simulation (SAS), which smoothly combines RANS and LES capabilities. The resulting flow fields are discussed along URANS, LES and corresponding measurements. The question arises, if SAS methods may combine advantages of RANS and LES methods for enclosed flow regimes with low turbulence but highly transient behavior. The first results show, that for evaluation of thermal comfort the use of hybrid models has advantages over URANS and plain LES and should therefore be preferred. Though SAS and LES calculations seem to under-predict turbulent viscosity and produce a small spreading rate of the inlet jets, which in turn results in an over-prediction of the core jet region. Standard URANS achieve a better correlation to the velocity magnitude at discrete measurement locations, but measured asymmetry in the flow field is not captured. process. Moreover, there might exist no steady solution on a fine mesh, so it is reasonable to let the RANS equation go unsteady with a gain in accuracy due to the resolution of some large movements. DES, on the other hand, uses a similar approach to SAS, which models the turbulence in boundary layers using RANS and resolves detached eddies. However, the switch between LES and RANS is dictated by the ratio of the corresponding length scales, i.e. by the grid. This high grid dependency makes DES almost not feasible for complex industrial geometries. In addition, pure LES allows calculations of the power spectrum, which supports the evaluation of the thermal comfort. Additional unsteadyness will occur in a real setup due to centrifugal forces. It is expected that these low frequency fluctuations will have a noticeable influence on the thermal comfort of passengers and therefore need to be known at the design process in advance.
Evaluation of SST-SAS model for industrial applications
2008
5 Seiten, 12 Bilder, 9 Quellen
Aufsatz (Konferenz)
Englisch
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